When David R. Obey, a Democrat, the third most senior member of the House and the chairman of the Appropriations Committee, announced he was retiring earlier this year, both parties rushed in. This independent, populist-leaning region, which includes some of the most wooded, northernmost parts of the state, had elected the same man for 40 years, so the fall has been unusual. Sean P. Duffy, a Republican and the district attorney from Ashland County – as well as a onetime cast member on the Real World, has encouragement from Tea Party activists among others. Julie Lassa, a state senator, is the Democratic Party’s choice.